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Oceans acidifying fastest in 300 million years due to emissions

LONDON — The Earth’s oceans may be acidifying faster than at any point during the last 300 million years due to industrial emissions, endangering marine life from oysters and reefs to sea-going salmon, researchers said.

The scientists found surging levels of carbon dioxide in the atmosphere forced down the pH of the ocean by 0.1 unit in the last century, 10 times faster than the closest historical comparison from 56 million years ago, New York’s Columbia University, which led the research, said Thursday. The seas absorb CO2 from the atmosphere, forming carbonic acid. The lower the pH level in the seas, the more acidic they are.

Past instances of ocean acidification have been linked with mass extinctions of marine creatures so the current one could also threaten important species, according to Baerbel Hoenisch, the paleoceanographer at Columbia who was lead author of the paper that appeared in the journal Science.

“If industrial carbon emissions continue at the current pace, we may lose organisms we care about — coral reefs, oysters, salmon,” Hoenisch said.

The UN’s Intergovernmental Panel on Climate Change has said ocean pH may fall another 0.3 units this century, according to Columbia. The closest change to the current pace occurred during the Paleocene-Eocene Thermal Maximum about 56 million years ago, when a doubling of the atmospheric concentration of carbon dioxide may have pushed pH levels down by 0.45 units over 20,000 years, according to the researchers.

Then, fossil records indicate as many as half of all species of seabed-dwelling single-celled creatures called benthic foraminifers became extinct, suggesting species higher up the food chain may also have died out, they said.

The scientists used fossil records including the preservation of calcium carbonate in ocean sediments and the concentrations of various elements to reconstruct past ocean conditions. Two other mass extinctions about 200 million years and 252 million years ago may also be linked to acidification, though there’s less fossil evidence, according to the study.

“Although similarities exist, no past event perfectly parallels future projections in terms of disrupting the balance of ocean carbonate chemistry — a consequence of the unprecedented rapidity of CO2 release currently taking place,” the researchers wrote.

Researchers based in the United States, Britain, Netherlands, Germany and Spain contributed to the study, which was funded by the U.S. National Science Foundation.